赤铁矿组织的显微力学性能及对球团强度的影响

球团矿的固结方式主要是赤铁矿的固相固结,即通过赤铁矿的再结晶互相连接,使球团具有一定的强度。为了研究赤铁矿形态对球团强度的影响,将球团矿内的赤铁矿按形态分为:大颗粒赤铁矿、互联状小颗粒赤铁矿和赤铁矿与磁铁矿交织结构。研究了2种球团中不同形态赤铁矿的显微硬度和断裂韧性,分析了不同形态赤铁矿的显微力学性能,进而探讨了赤铁矿形态对球团矿强度影响的机理。实验结果表明,大颗粒赤铁矿和赤铁矿与磁铁矿交织结构具有很好的综合显微力学性能。在球团氧化焙烧过程中,应适当增加残存磁铁矿的比例,以增加交织结构在球团矿内的含量;同时尽可能增加赤铁矿再结晶互联时间,以改善赤铁矿的互联状况,促进大颗粒赤铁矿的形成,从而提高球团矿的抗压强度。     

蛇纹石对磁铁矿和赤铁矿球团的影响

研究了蛇纹石对磁铁矿和赤铁矿2种不同矿粉球团的生球质量、抗压强度和冶金性能的影响。结果表明：配蛇纹石后赤铁矿和磁铁矿球团的生球质量都得到改善。配蛇纹石后磁铁矿和赤铁矿球团预热强度都下降,在相同温度和蛇纹石质量分数下,赤铁矿球团预热强度比磁铁矿球团低50~100 N/个,在焙烧温度小于1280 ℃时,随着蛇纹石质量分数的增加,磁铁矿和赤铁矿球团抗压强度都下降,但在1300 ℃的温度下,配蛇纹石的球团抗压强度比基准期球团抗压强度高。配蛇纹石后磁铁矿和赤铁矿球团还原膨胀率都下降。蛇纹石质量分数为1.5%时,球团矿还原度相对高。     

内配碳赤铁矿球团固结机理研究

以赤铁矿为原料,添加适量的固体燃料可以提高球团矿强度,大幅度降低焙烧燃耗,改善球团矿的冶金性能.研究碳对赤铁矿球团强度的影响,结合显微结构分析,揭示内配碳赤铁矿球团的固结机理.结果表明,内配碳赤铁矿球团焙烧过程中存在部分原生赤铁矿先被还原成磁铁矿或浮士体,然后再氧化成次生赤铁矿的过程.次生赤铁矿活性高,易发生迁移和扩散...     

以赤铁矿为主配加磁铁矿制备氧化球团的研究

采用正交试验,研究赤铁矿配加磁铁矿制备氧化球团的影响因素。试验结果表明：赤铁矿添加30％磁铁矿后,球团矿适宜预热温度由980℃降低到880C,焙烧温度由1330℃降低到1280℃,且成品球团抗压强度明显提高。模拟扩大试验研究表明：当预热温度为900℃、预热时间10min、焙烧温度为1280～1300℃、焙烧时间20min时,磁铁矿配比从0提高到30％,预热球团抗压强度从377N／个提高到966N／个,成品球团抗压强度从2509N／个提高到3045N／个,氧化球团矿的冶金性能也得到改善．可作为优质高炉炉料。     

第五讲 球团矿固结过程基础(续一)

三、磁铁矿球团氧化焙烧的特性磁铁矿球团在氧化焙烧时,由于磁铁矿本身具有的理化性质就产生了赤铁矿球团在氧化焙烧时所没有的特性。掌握了解这些特性,对创造最佳焙烧工艺制度以生产优质球团是极有价值的。     

内配碳赤铁矿球团反应动力学及其模型

研究了碳对内配固体燃料赤铁矿球团焙烧过程的影响，研究表明，球团矿内各种反应是同时进行的，各自的反应速度地是相互独立的，提出了该反应体的过程模型，试验结果及模型计算表明，在内配固体燃料赤铁矿团焙烧过程中存在赤铁矿先被还原成磁铁矿或浮士体，然后再氧化成赤铁矿的现象，为改进赤铁矿球团的焙烧工艺提供了理论基础。     

磁铁矿球团焙烧热分析

本文通过热分析研究了磁铁矿球团的高温固结。当温度到一定水平时发现磁铁矿转变为赤铁矿的过程逆转（后者分解成前者）。同时也对添加剂和脉石成份对赤铁矿热分解的影响进行了研究。     

氧化过程对钛磁铁精矿球团焙烧固结的影响

本文主要论述攀枝花钛磁铁精矿球团焙烧固结过程与生球氧化的关系。研究工作是在φ300×900毫米间歇式回转窑中进行的。试验研究表明:攀枝花铁精矿球团的氧化与球团高温焙烧固结机理有着密切的关系。生球氧化不充分,由于球核未氧化的磁铁矿的再结晶,与球团表层氧化生成的赤铁矿再结晶的不同结构产生环状同心裂纹,使球团的抗压强度低于100公斤/个。保证生球完全氧化,然后靠着赤铁矿在高温条件下(1250～1280℃)的再结     

磁铁矿球团氧化机理的研究

磁铁矿球团高温恒温氧化时，氧气向球团的扩散为限制性环节，低温恒温氧化或升温氧化，球团内磁铁矿颗粒氧化为限制性环节。磁铁矿颗粒氧化按温度划分为两段。在较低温度下主要是铁离子扩散，较高温度下氧离子扩散的扩散能力增强。     

赤铁矿内配兰炭生产球团矿固结机制研究

摘要：通过对不同温度、不同兰炭配入量的内配兰炭赤铁矿球团进行FeO含量检测和矿相结构分析,得出兰炭在赤铁矿球团焙烧过程中的作用机制。结果表明：兰炭含量较低时,主要发生燃烧反应,不利于赤铁矿向磁铁矿转变,且气孔率增大使球团抗压强度降低;兰炭含量过高,还原反应占主导,大量Fe2O3被还原为Fe3O4,甚至被还原为FeO,随之形成铁橄榄石;兰炭燃烧放热过多使球团内部熔化,导致球团抗压强度大幅降低。最终选择适宜的兰炭配比为1.5%,焙烧温度为1300℃,焙烧时间为18.5min,空气流量为3.2L/min, 抗压强度为2708.8N。     

Magnetite Particle Size Distribution and Pellet Oxidation

Oxidation of magnetite pellets is commonly performed to prepare strong pellets for ironmaking. This article presents a contribution to quantitative understanding of fundamental pellet oxidation kinetics, based on measured oxidation kinetics of magnetite particles and pellets. The commonly observed “plateau” oxidation behavior is confirmed to be consistent with the effect of very large differences in magnetite particle sizes in the concentrate from which pellets are produced. The magnetite particles range in size from less than a micron to several tens of a microns; changing the size distribution by inert sintering of pellets decreases both the plateau level of oxidation and the specific surface area, in ways that are compatible with an assumed Rosin-Rammler magnetite particle size distribution.     

提高高硫精矿球团矿强度的途径

以安庆含硫１．６１％的磁铁精矿为对象,研究了用高硫磁铁精矿制备满足高炉冶炼要求的氧化球团矿的可行性。采用含镁工业盐类矿物为添加剂,通过系统地试验研究,获得了抗压强度２５５２Ｎ／个、含硫量０．０１８％、ＦｅＯ含量１．６７％、冶金性能良好的球团矿。探讨了添加剂强化高硫磁铁精矿球团氧化固结的机理。     

MgO含量和来源对球团焙烧特性及冶金性能的影响

分别以5种不同的含镁添加剂（高镁磁铁矿、镁橄榄石、白云石、菱镁石和氧化镁粉）制备镁质球团,阐述MgO含量和来源对磁铁矿球团焙烧特性及冶金性能的影响。研究结果表明:不同的含镁添加剂对于生球的落下强度有着一定影响,其中氧化镁粉与高镁磁铁矿均能够提高球团的落下强度。相同的预热焙烧制度下,提高MgO含量会增加球团孔隙率,降低预热和焙烧球团的抗压强度,其中白云石对焙烧球团强度的不利影响最小。增加预热球团的氧化度有利于促进镁质焙烧球团固结,提高其抗压强度。在MgO来源相同的情况下,MgO含量的增加会导致球团孔隙的增减,降低了球团强度,而配加不同种类的含镁添加剂,均能不同程度改善球团的还原膨胀性、低温还原粉化性和还原性,其中配加高镁磁铁矿的球团的还原膨胀性和低温还原粉化性均优于于其他含镁球团。      

LEACHING RATES OF ICEL-YAVCA DOLOMITE IN HYDROCHLORIC ACID SOLUTION

Additives can give rise to obvious, step-wise changes both in the oxidation process and in the sintering process. Therefore, the oxidation and sintering characteristics measured in dried pellets prepared from pure magnetite concentrates can not be representative for those characteristics in dried pellets containing additives. The oxidation and sintering characteristics of magnetite iron ore pellets balled with a novel complex binder (namely MHA) were mainly investigated by batch isothermal oxidation measurements in this research. Combined results reveal that the thermal decomposition of MHA binder influences the oxidation and sintering processes of dried pellets. Oxidation rate of pellets increases obviously with increasing the oxidation temperature in the range from 800°C to 1000°C. And the remaining FeO content declines gradually when separately heated for 10 min at low temperature (<1000°C). However, the oxidation rate of pellets decreases distinctly when oxidation temperature is higher than 1000°C. In addition, when oxidation temperature increases from 1000°C to 1250°C, the FeO content of pellets goes up obviously, particularly at 1250°C. The FeO content in the core of sintered pellets heated at 1250°C can even reach 29.68%. SEM spectrum analysis demonstrate that some iron appears in forms of wustite in sintered pellets, which indicates that the reduction reaction of iron oxide occurs during the high temperature sintering process. This is explained by the occurrence of reducing atmospheres because of the pyrogenic decomposition of MHA binder.     

Effect of MgO on Oxidation Process of Fe3 O4 in Pellets

Induration process of oxidized pellets involves the oxidation of Fe3 O4 and re-crystallization of Fe2 O3 .The oxidation process of Fe3 O4 is significant for pellets to obtain better ambient strength.Thus,the effect of MgO on oxidation process of Fe3 O4 was investigated.The unreacted core model was applied to analyze the oxidizing indura-tion process of pellets.The experimental results show that MgO plays a negative role in the oxidation process of Fe3 O4 .The oxidation rate of Fe3 O4 in MgO-fluxed pellets (95.0% Fe3 O4+5.0% MgO)is slower than that in standard acid pellets (100% Fe3 O4 ).The relation between oxidation ratio of Fe3 O4 and time was calculated based on the unreacted core model for both MgO-fluxed pellets and standard acid pellets.According to verification experi-ments,the values calculated by model coincide well with the experimental values.Therefore,the unreacted core model could be applied to describe the oxidizing induration process of pellets.     

Oxidation of iron ore at moderate and high temperatures

The oxidation of magnetite and titanomagnetites in iron-ore sinter at moderate (400–1000°C) and high (1000–1350°C) temperatures is subjected to physicochemical analysis. The oxidation kinetics is studied on briquets of Olkhovsk magnetite concentrate and Kachkanar titanomagnetite concentrate, as well as samples of unfluxed Kachkanar pellets and pellets fluxed to a basicity of 1.3. At moderate temperatures, the limiting stage in oxidation is the diffusion of the reagent to sections of the surface smaller than the total spherical surface. At high temperatures, in both isothermal and nonisothermal conditions, the limiting stage in oxidation is the diffusion of oxygen in pellet pores. From the kinetic equations for isothermal oxidation, the apparent activation energy with the specified degree of conversion is calculated; its variation is associated with change in the type of reagent diffusion through the layer of reduction products. The apparent diffusion coefficients of oxygen in Kachkanar pellets are determined at 500–1000°C. A method has been developed for determining the degree of pellet oxidation as a function of the time and the temperature in nonisothermal conditions. This method may be used to calculate the oxidation of the pellets in roasting on conveyer machines. The results may be used to determine the degree of oxidation in the roasted pellet bed and to optimize the heat-treatment parameters in roasting systems.     

含NaOH碱性钒钛磁铁矿球团矿的制备

 为了更好地探究钒钛磁铁精矿碱性球团低温还原熔分工艺,用钒钛磁铁精矿和焦粉为主要原料制备钒钛磁铁矿碱性球团,考察了加水量、成球压力、黏结剂加入量和NaOH含量对球团落下强度的影响及焙烧温度对球团抗热裂性的影响。结果表明:钒钛磁铁矿碱性球团的落下次数随成球压力、聚乙烯醇浓度和NaOH加入量的增加而增加,随加水量的增加呈先增加后减小的趋势变化;最佳成球工艺参数为水加入量为6%,黏结剂聚乙烯醇浓度为0.4%,成球压力为10 MPa,NaOH加入量为4%;在最佳的碱性球团制备工艺参数下考察了生球和干球的抗热裂性,两者随温度升高都变差,但是同温度下干球的抗热裂性优于生球的热裂性能。     

Effect of TiO2‐content on Reduction of Iron Ore Agglomerates

The effect of titanium oxide on iron ore agglomerates is studied by the use of test sinter, test pellets and synthetic briquettes under laboratory conditions. Titanium favours secondary hematite rather than magnetite, which is the main phase in the sinter of Rautaruukki's Raahe plant. Additionally, the effects of sinter RDI and pellet LTD on the blast furnace process are evaluated using the test results of basket trials in LKAB's Experimental Blast Furnace. The effect of titanium in synthetic hematite is studied as hematite is reduced to magnetite in the RDI test. This occurrence causes deterioration in burden permeability. Synthetic titanium‐bearing iron oxides under controlled conditions are investigated at the University of Oulu. The effect of TiO₂, in solid solution in magnetite, on the magnetite to hematite oxidation is studied separately in order to simulate the final stage of the sintering process. In other experiments, hematite samples doped with various contents of TiO₂ are studied using thermogravimetry under a controlled gas atmosphere (CO/CO₂/H₂/N₂). The TiO₂ content of hematite has a clear effect on reduction degradation. Also increasing content of TiO₂ in solid solution in magnetite radically accelerates the oxidation rate. In the pilot tests, TiO₂ content has a similar negative effect on the reduction strength of both sinter and pellets     

Sintering characteristics and kinetics of acidic haematite ore pellets with and without mill scale addition

Haematite ore pellets require very high induration temperature (>1573?K) while, magnetite ore pellets require much lower temperature due to the oxidation of magnetite during induration. Mixing of some magnetite in haematite ore can improve the sintering property of pellets during induration. Mill scale is a waste material of steel plant which contains mainly FeO and Fe₃O₄. It can also be blended in haematite ore pellet mix which can enhance diffusion bonding and recrystallisation bonding and facilitate sintering at the lower temperature like magnetite ore. The extent of improvement in sintering property, sintering mechanism and its kinetics in the presence of mill scale is very imperative to study. In current study, the sintering characteristics of acidic iron ore pellet with 15% mill scale and without mill scale has been studied separately through microstructure observation, apparent porosity measurement and volume change. The volume changes due to heating at varying temperature and time has been measured by mercury displacement method and the data has been exploited for sintering kinetics study, wherein, extent of sintering α has a power relation with time. Several kinetics parameters such as time exponent (n), rate constant (k) and activation energies have been estimated for above two pellets and compared. While acidic pellet without mill scale requires 385?k?cal?mol^?1, acidic pellet with 15% mill scale requires only 310?k?cal?mol^?1 activation energy.